SC732 is a two channel servo controller.
- SC732 – Assembly guide
- SC732 – Compatibility
- SC732 – Parts list
- SC732 – Printed circuit board
- SC732 – User guide
- SC700 series information
- SC700 series support
Downloads
- SC732, v1.0, Kit contents sheet (PDF)
- SC732, v1.0, Schematic (PDF)
- SC732, v1.0, PCB design files (OSHWLab)
- SC732, v1.0, Gerber files (ZIP)
Errata
Nothing known
Suppliers
| Kits | Website | From | Currency |
| Small Computers Direct | SCDirect | UK | GBP |
| Stephen C Cousins | Tindie | UK | USD |
| Small Computer Central | Lectronz | UK | Euro/USD |
| PCBs | Website | From | Currency |
| Small Computers Direct | SCDirect | UK | GBP |
| Stephen C Cousins | Tindie | UK | USD |
| Small Computer Central | Lectronz | UK | Euro/USD |
| Assembled and Tested | Website | From | Currency |
| Not available | |||
| Components | |||
| See parts list |
Tindie does not collect VAT for EU countries
Lectronz does collect EU VAT for orders up to 150 EUR
10 REM Servo demo program
20 FOR Z=1 TO 30
21 NEXT Z
30 IF A<115 OR A>230 THEN A=115
40 IF B<115 OR B>230 THEN B=230
50 OUT 6,A
60 OUT 7,B
70 A=A+1
80 B=B-2
90 GOTO 20
Demonstration Video (MP4, 20MB)
Parts List
| Reference | Qty | Component |
| PCB | 1 | SC732, v1.0, PCB |
| C1 to C10 | 10 | Capacitor, ceramic, 100 nF |
| C11 | 1 | Capacitor, electrolytic, 100 µF |
| JP1 | 1 | Header, male, 2 x 8 pin, angled |
| Jumper | 8 | Jumper shunt |
| P1 | 1 | Header, male, 2 row x 40 pin, angled |
| P2+3+4+5 | 1 | Header, male, 1 x 14 pin, angled |
| RN1 | 1 | Resistor network, 8x100k, SIL, 9-pin |
| Screw (for spacer) | 1 | Machine screw, 6mm, M3 |
| Spacer | 1 | Spacer, 10mm, M3, nylon |
| U1, U4, U5 | 3 | 74HCT688 |
| U2, U3 | 2 | 74HCT273 |
| U6, 7 | 2 | 74HCT393 |
| U8 | 1 | 74HCT139 or 74AHCT139 |
| U9 | 1 | 74HCT74 |
| X1 | 1 | Oscillator 1.8432 MHz |
| IC socket 20-pin U1 to U5 | 5 | Socket, DIP, 20-pin |
| IC socket 16-pin U8 | 1 | Socket, DIP, 16-pin |
| IC socket 14-pin U6, U7, U9, X1 | 4 | Socket, DIP, 14-pin |
Printed Circuit Board
User Guide
SC732 is a two channel servo controller. It has tight address decoding and easy access with a single OUT instruction to set each servo position.
The address decoding is such that one module takes only two I/O addresses (one for each servo channel). Only writes to those addresses are decoded, so those addresses could be allocated to another device that only has a read function. Many of these modules can be installed in a single system as long as there are no address conflicts.
The output of each channel is set by writing a value from 0 to 255 decimal to the port address of the servo channel. A value of zero turns the pulses off, leaving the output signal at a steady low level. A value of 1 produces the most narrow pulse and 255 the most wide pulse.
Typically, a servo requires a pulse between 1 ms and 2ms. The pulse needs to be repeated about 50 times a second. If no pulse is detected the servo will not move. With a 1.8432 MHz oscillator fitted, a 1 ms pulse is produced when a value of 115 is written to the servo port and a 2 ms pulse is produced by the value 230. The pulses are repeated every 17.8 ms (56.25 Hz).
These figures are derived from the following:
The oscillator is divided by 16 to produce the clock for an 8 bit ripple counter. After 256 clock pulses the ripple counter resets to zero. The rate of counter resets is then divided by 8 to give the repeat frequency.
- Ripple counter clock = 1.8432 MHz / 16 = 115200 Hz
- Ripple counter reset frequency = 115200 / 256 = 450 Hz
- Pulse repeat frequency = 450 / 8 = 56.25 Hz
Examples
If the base I/O address is set to 6, then to set the value of the servo pulse width you need to write the value to I/O address 6. Servo #2 width is set at I/O address 7.
To set the width of servo #1 channel to 200 (decimal) in BASIC:
OUT 6, 200
To set the width of servo #1 channel to 200 (decimal) in assembler:
LD A, $C8
OUT (6), A
Input/output port functions
| RCBus I/O Address | Read | Write |
| Configurable *1 base address | n/a | Write servo value |
- The RCBus I/O address should be set to any even address. Typically, this might be 0x06 (6 decimal). Many of these modules can be included in a single system as long as there are no address conflicts.
Jumper options
| Jumper | Function |
| JP1 | Set SC732’s RCBus I/O address |
| P4 | Set servo power source (typically 5 volts) P4.1-2 Power from computer’s 5 volt supply P4.2-3 Power from external source (P5) While the option is available to power the servo(s) from the computer’s 5 volt supply it is highly recommended that an external supply be used due to noise and loading issues |
Frequencies
The following table gives the frequencies and timings for a range of oscillator frequencies.
| JP 2 position | Oscillator 1.8432 MHz | Oscillator 2.000 MHz | Oscillator 1.024 MHz |
| Oscillator frequency | 1843200 Hz | 2000000 Hz | 1024000 Hz |
| Ripple counter clock | 115200 Hz | 125000 Hz | 64000 Hz |
| Ripple counter reset rate | 450 Hz | 488.28 Hz | 250 Hz |
| Pulse repeat frequency | 56.25 Hz | 61.04 Hz | 31.25 Hz |
| Pulse repeat time | 17.78 ms | 16.38 ms | 32.00 ms |
| 1 ms pulse width value | 115 | 125 | 64 |
| 2 ms pulse width value | 230 | 250 | 128 |
| 1.5 ms (mid position) | 173 | 188 | 96 |
Assembly Guide
Below is the suggested order of assembly. A general guide to assembling circuit boards can be found here.
- Decoupling capacitors C1 to C10 (100 nF)
These can be fitted either way around - Header pins P2 + P3 + P4 + P5 (1 row x 14 pin, angled)
This can be fitted as a single strip if a few pins are removed - Sockets for U1 to U9
Fit such that the notch in the socket matches the curve in the outline on the PCB silkscreen - Socket for X1 (optional)
Not recommended as the oscillator is quite large and could touch other modules - Resistor network RN1 (8 x 100k)
This must be fitted the correct way around whereby the dot on the component matches the dot on the PCB silkscreen - Bus header P1 (2 row x 40 pin, angled)
Make sure the pins are parallel to the PCB so that the board is vertical when it is fitted into a backplane socket - Header pins JP1 (2 row x 8 pin, angled or straight)
- Capacitor C11 (100 uF)
This must be fitted the correct way around, as described here - Insert the integrated circuits into their sockets
Make sure the notch in the component is at the end indicated by the notch in the socket and the curve on the PCB silkscreen - Fit oscillator X1 (1.8432 MHz)
- Fit the nylon spacer in the mounting hole
Fit jumper shunts in the positions shown below. All other jumpers are optional and should only be fitted if the feature is required.
Compatibility
This module conforms to the RCBus specification v1.0 for RCBus-2014 and RCBus-Z80.
The RCBus specification includes RCBus-2014 (both RC2014 standard 40-pin bus and RC2014 enhanced 60-pin bus) and also the full 80-pin RCBus. The 80-pin RCBus provides support for advanced Z80 features, such as the interrupt daisy-chain, as well as support for other processor families.
The table below indicates electrical compatibility with each backplane type (40, 60 and 80 pin)
| Backplane | ? | Compatibility notes |
| RCBus 80-pin |  | Fully supported |
| RCBus 60-pin (RC2014 enhanced) | | Fully supported |
| RCBus 40-pin (RC2014 standard) | | Fully supported |
The following table indicates electrical compatibility with SC732. Check firmware and software details for any required software support.
| Product (80-pin) | ? | Compatibility notes |
| SC126 Z180 motherboard | | Adds Z180 SBC motherboard |
| SC701 Backplane 6+1 | | Adds 6 module sockets RCBus 80-pin |
| SC702 Backplane 6+1 | | Adds 6 module sockets RCBus 80-pin |
| SC703 Power from 12v | | Adds power supply 8 to 15 volts input |
| SC704 I2C bus master | | Adds I2C bus master and I2C EEPROM |
| SC705 Serial ACIA | | Adds one serial port Typically set to 0x40 |
| SC706 Z80 CPU | | Adds Z80 CPU and clock oscillator |
| SC707 Memory 128k | | Adds 128kB RAM and 128kB ROM |
| SC708 Z80 SBC | | Adds single board Z80 computer |
| SC709 Backplane 12+1 | | Adds 12 module sockets RCBus 80-pin |
| SC710 Backplane 12+1 | | Adds 12 module sockets RCBus 80-pin |
| SC711 Prototyping | | Prototyping module |
| SC712 Power from 5v | | Adds power supply 5 volts input |
| SC713 RCBus tool | n/a | Simple reference tool No electrical function |
| SC714 Memory 512k | | Adds 512kB RAM and 512kB flash ROM |
| SC715 Compact flash | | Adds Compact Flash storage |
| SC716 Z80 SIO/2 | | Adds two serial ports Typically set to 0x84 |
| SC717 Z80 PIO | | Adds parallel I/O using Z80 PIO |
| SC718 Z80 CTC | | Adds counter/timer using Z80 CTC |
| SC719 Digital I/O | | Adds digital I/O Eight in, eight out |
| SC720 Z80 motherboard | | Adds Z80 SBC motherboard |
| SC721 Memory 512k | | Adds 512kB ROM and 512kB RAM |
| SC722 Z180 CPU | | Adds Z180 CPU and serial ports |
| SC723 Backplane 3 | | Adds 3 module sockets RCBus 80-pin |
| SC724 Breakout | | Prototyping breakout module |
| SC725 SIO+CTC | | Adds two serial ports and 4 counter/timers |
| SC726 Clock generator | | Generates CLK and CLK2 bus signals |
| SC727 Real time clock | | Adds real time clock for time and date |
| SC728 Module riser | | Simple module riser for RCBus 80-pin |
| SC729 Compact flash | | Adds Compact Flash storage |
| SC730 Z80 CPU + MMU | | Adds Z80 CPU with clock and MMU |
| SC731 Dual PWM generator | | Adds dual PWM signal generator |
| SC732 Dual servo controller | | Multiple modules can be used |
| SC791 Z80 system | | Adds modular Z80 computer |
| SC792 Z180 system | | Adds modular Z180 computer |
| Product (40 pin) | ? | Compatibility notes |
| SC114 Z80 motherboard | | Adds Z80 SBC motherboard |
| SC130 Z180 motherboard | | Adds Z180 SBC motherboard |
| SC133 Backplane 11+1 | | Adds 11 module sockets RCBus 40-pin |
| SC134 LED output port | | Adds eight LED outputs |
| SC135 Digital output port | | Adds eight digital outputs |
| SC136 Digital input port | | Adds eight digital inputs |
| SC137 I2C bus master | | Adds I2C bus master |
| SC139 Serial ACIA | | Adds one serial port Typically set to 0x40 |
| SC141 Backplane 12+1 | | Adds 12 module sockets RCBus 40-pin |
| SC142 Power from 12v | | Adds power supply 8 to 15 volts input |
| SC143 Flash ROM | | Adds 128kB ROM in four 32kB banks |
| SC145 Compact flash | | Adds Compact Flash storage |
| SC147 Backplane 6+1 | | Adds 6 module sockets RCBus 40-pin |
| SC148 Power from 5v | | Adds power supply 5 volts input |
| SC149 Z80 CPU | | Adds Z80 CPU and clock oscillator |
| SC150 Paged RAM 128k | | Adds 128kB RAM in two 64kB banks |
| SC151 Paged ROM 128k | | Adds 128kB ROM in four 32kB banks |
| Other suppliers | ? | Compatibility notes |
| RC2014 Mini system | | Adds Z80 SBC motherboard |
| RC2014 Pro system | | Adds modular Z80 computer |
| RC2014 Zed system | | Adds modular Z80 computer |
| RC2014 Micro module | | Adds Z80 SBC computer |
| RC2014 Backplane 5 | | Adds 5 module sockets RCBus 40-pin |
| RC2014 Backplane 8 | | Adds 8 module sockets RCBus 40-pin |
| RC2014 Backplane Pro | | Adds 12 module sockets RCBus 60-pin |
| RC2014 Z80 CPU | | Adds Z80 CPU module |
| RC2014 SIO/2 dual serial | | Adds two serial ports at address 0x80 to 0x87 |
| RC2014 Compact flash | | Adds Compact Flash storage |
| RC2014 Dual clock | | Generate CLK2 only Conflict on CLK signal |
| RC2014 Pageable ROM | | Adds pageable ROM module |
| RC2014 64k RAM | | Adds pageable RAM module |
| RC2014 Memory 512k | | Adds 512kB RAM and 512kB flash ROM |
| RC2014 Digital I/O | | Adds eight LED outputs and eight push buttons |
| RC2014 Real time clock | | Adds real time clock for time and date |
| RC2014 RP2040 VGA terminal | | Connect VGA monitor and USB keyboard |
| RC2014 Pi Pico terminal | | Connect VGA monitor and USB keyboard |
| RC2014 YM2149 sound card | | Adds authentic retro sound |
| Weird electronics Flock v2 | | Adds floppy disk and real time clock |
Notes
- This product is designed for hobby use and is not suitable for industrial, commercial, or safety-critical applications.
- The product contains small parts and is not suitable for young children.
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